An internal combustion engine typically employs camshaft(s) to open and close the engine's valves in order to control a supply of intake of air to the cylinder for combustion therein and removal of post-combustion gas therefrom. A camshaft-drive element, such as a timing belt or a timing chain, is frequently used to synchronize the rotation of an engine's crankshaft and camshaft(s) so that the engine's valves open and close at proper times during each cylinder's intake and exhaust strokes.
A timing belt usually includes teeth on the surface that contacts camshaft and crankshaft sprockets, while a timing chain typically includes rolling elements for contact with such sprockets. In certain engine designs, the timing belt or chain is also employed to maintain safe running clearance between the engine's valves and pistons. Additionally, in some engine designs the timing belt or chain may be used to drive other engine components, such as a water and/or oil pump.
A tensioner is frequently used in an engine with either the timing belt or chain. Such a tensioner generally applies a force to the timing belt or chain to maintain the belt or chain in tension and, therefore, the rotational timing between the engine's crankshaft and camshaft(s). The tensioner ensures that, independent of the motion of the belt or chain, the connection between the engine's crankshaft and camshaft(s) remains intact, while limiting stress on the related components.